In the preparation of silver halide photographic materials, coloration of photographic emulsion layers or other layers is often effected for the purpose of absorbing light falling within a particular wavelength range.
If it is necessary to control the spectral composition of the light penetrating into photographic emulsion layers, a colored layer is provided on the support in a position farther from the support than photographic emulsion layers. The colored layer of the kind is called a filter layer. In the case of a multi-layered color photographic material having a plurality of photographic emulsion layers, the filter layer may be positioned intermediate between those emulsion layers.
Blur of images (i.e., halation) may be caused by re-penetration of light which scatters during or after passing through photographic emulsion layers and is reflected on the interface between the emulsion layer and the support or on the surface of the photographic material opposite to the emulsion layer, into the photographic emulsion layers. This may be prevented by a colored layer provided between the photographic emulsion layer and the support or on the surface of the support opposite to the photographic emulsion layer. The colored layer is called an anti-halation layer. In the case of a multi-layered color photographic material, the anti-halation layer may be provided intermediate between the respective layers.
For the purpose of preventing lowering of the image sharpness caused by scattering of light in photographic emulsion layers (this phenomenon is generally called "irradiation"), coloration of photographic emulsion layers is also often effected.
The layers to be colored for these purposes are mostly hydrophilic colloid layers, and in general, water-soluble dyes are incorporated into the layers so as to color them. The dyes must satisfy the following conditions:
(1) they have a suitable spectral absorption in accordance with their use and the object;
(2) they are photochemically inactive. That is to say, they do not have any harmful influence on the chemical properties of silver halide photographic materials. For example, they do not lower the sensitivity of the materials, they do not cause latent image fading, and they do not cause fogging;
(3) they are decolored or dissolved out during the step of photographic processing of the photographic materials which contain them, so that they do not leave any harmful coloration on the processed photographic materials; and
(4) they have an excellent time-dependent storage stability in solutions or in photographic materials.
Many dyes have heretofore been known to satisfy these conditions, and to absorb visible rays or ultra-violet rays. They are suitable for improving the images formed in conventional photographic elements which are sensitized to be sensitive to lights having a wavelength of 700 nm or less. In particular, triarylmethane and oxonole dyes have been used widely.
On the other hand, there is a need for anti-halation and anti-irradiation dyes capable of absorbing light falling within the infrared spectral range for near-infrared sensitized recording materials, for example, for photographic recording materials for recording output with near-infrared lasers.
For instance, one means of exposing photographic materials of this kind is an image forming method by a so-called scanner system. Specifically, an original is scanned and a silver halide photographic material is exposed on the basis of the resulting image signal, so as to form a negative image or positive image corresponding to the image of the original on the photographic material.
Among the recording light sources for such a scanner recording system, semiconductor lasers are used most favorably. Devices for semiconductor lasers are small-sized and low-priced and may easily be modulated. In addition, semiconductor lasers have a longer life than other He-Ne lasers or argon lasers. Moreover, since they emit infrared rays, a light safelight may be used in handling infrared-sensitive photographic materials. Therefore, semiconductor lasers are advantageous with respect to handlability and operability.
However, since no suitable dye is known which absorbs light falling within the infrared spectral range and which satisfies the preceding conditions (1), (2), (3) and (4), especially conditions (3) and (4), there are few photographic materials having a high light sensitivity in the infrared range and having excellent anti-halation and anti-irradiation properties. Therefore, at the present, the characteristics of the semiconductor lasers having the above-mentioned excellent capacity cannot be fully utilized.
Until now, various efforts have been made to find dyes satisfying the preceding conditions, and many dyes have heretofore been proposed.
For instance, examples include the tricarbocyanine dyes described in JP-A-62-123454, JP-A-63-55544, JP-A-64-33547 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"); the oxonole dyes described in JP-A-1-227148; the merocyanine dyes described in JP-A-1-234844; the tetra-aryl type polymethine dyes described in JP-A-2-216140; and the indoaniline dyes described in JP-A-50-100116, JP-A-62-3250, JP-A-2-259753.
However, there are few dyes which sufficiently satisfy all the preceding conditions.